Drive pawl for electromagnetically wound timepieces



Nov. 26, 1968 E.GJ UNZ I 3,412,630

DRIVE PAWL ELECTROMAGNETICALLY WOUND TIMEPIECES Filed April 24, 1967 Fig. 1

United States Patent 4 Claims. 61. 14-577 ABSTRACT OF THE DISCLOSURE In an electrically wound spring powered timepiece a floating pawl is loosely carried on a ratchet toothed driver wheel of the work train for being kicked in the direction of slippage as the spring is wound and effecting coupling of the spring to the driver wheel as the spring unwinds in the opposite direction to power the train. The pawl has an arcuate portion having interior teeth meshing with those of the driver, which portion is urged radially inwardly by a bow spring against the driver wheel shaft. In the invention the conventional oscillatory disc carrying an end of the spring need not be axially alined with the driver wheel, to give uniform urging of the pawl on the ratchet wheel.

BACKGROUND OF THE INVENTION Field of the inventi0n.This invention relates to pawls for use in electrically wound timepieces as the working connection between a periodically stressed power spring and the work train.

Description of the prior art.-Paw1s of the nature are shown in Patent No. 3,115,788. The winding and drive mechanism of such a clock includes an oscillatory disc turnable on a shaft with the outer end of a coil drive spring fixed to the periphery of the disc and the inner end to the shaft. When a prewound spring unwinds to run down position, contacts are closed to energize an electromagnet so as to kick the disc to turn about the shaft and wind the spring. During this windup turning of the disc, the pawl carried on the disc, rides in non-locking direction over ratchet teeth on a driver wheel of the work train. When the disc stops turning, the pawl digs into the teeth so as to transmit the spring power torque to the work train. This is all well known in the art.

The driver pawl is one of the most troublesome and expensive elements in an electrically wound timepiece. Conventionally it was in the form of an impact push pawl which was urged into engagement with ratcheted teeth by a coil spring. This form of construction demanded that the urge on the pawl not be too great, because during spring wind-up the work train might be stopped. Neither could the urging of the ratchet on the teeth be too small as this led to jumping and non-engagement. In spite of accurate finishing it was not possible to hold the urging pressure within the desired tolerances. To utilize this type of pawl and get satisfactory results required very narrow limits of tolerance and production costs were relatively high. Also the assembly was complicated and expensive. The pawl was mounted on the disc and if the disc were not exactly axially alined with the shaft carrying the ratcheted drive wheel the urging pressure on the pawl would vary as disc and shaft turned, with the consequent results mentioned above due to both excessive and inadequate urging. Moreover such a pawl was quite noisy.

SUMMARY OF THE INVENTION The above drawbacks are minimized in an electrically wound timepiece wherein the pawl is the working connection between the oscillatory disc with a periodically pretensed drive spring and the work train. The pawl is of a floating type, T shaped and of L-shaped longitudinal cross-section having a loose fitting pin-in-slot power transmission, not turnable but loosely fitting, on the main driven shaft of the work train. The pawl has a set of inner teeth fitting almost exactly with outer teeth of a Wheel on the main powered shaft of the work train. A predetermined pressure or urging of the set of the inner teeth on the outer is effected by a slightly bowed spring substantially attached at its ends to the pawl and having its mid portion urged against the main driven shaft.

DRAWING FIG. 1 shows a longitudinal diametric cross section of the pawl, driven portion of work train and disc and FIG. 2 shows the pawl disposed over the outer face of a ratcheted main drive wheel.

DESCRIPTION The oscillated disc 1 on which an unshown periodically rewound drive spring engages is bearing mounted on the shaft 2. The wind-up direction of the disc 1 is shown by the arrow in FIG. 2. By means of the pawl the torque of the disc turns the drive wheel 6 of the train of works; the drive wheel 6 is provided with peripheral ratchet teeth 10 and is secured fast on a shaft 5 by means of a fluted portion 7. A plastic pawl in the general shape of a T having a shank 4' and cross section 4" and generally designated 4 and of L-shaped cross section along the shank is bearingly mounted loosely on the same shaft 5 which passes through slot shaped aperture 11 in the portion 4". A pin 3 on the peripheral portion of the oscillated disc projects parallel with shaft 5 and engages in a receiving slot 8 in the end of the shank of the pawl body 4. The upstanding portion 9 of the pawl body is provided with inner ratchet teeth 9 mating with the teeth 10 on the driver wheel 6.

A pressing force of the pawl body in the direction of the shaft 5 is produced by means of a normally flat spring 12 whose ends 14 are received in laterally right angled slots 15 in lugs 15a on the pawl body about diametrically opposite from each other with respect to the shaft axis. However, the lug slots 15 are so spaced from the diameter that the mid portion of the spring is bent out of line and resiliently bears against the shaft 5 in the circumferential groove 5 thereof to urge the teeth 9 on the upstanding part against those on the wheel 6. The end faces of the right angled slots retain the spring against longitudinal movement and resultant loss of the spring, while deeply notched ribs 13 opening away from portions 9' receiving the spring urged into the groove enable the spring to hold the pawl on the shaft 5.

The combination has many special advantages. Among these is that a wide tolerance in axial alinement of the oscillated disc and the driver is possible without influence of pressure of the pawl normal to the driver wheel. Jumping over the driver wheel teeth is not possible. The radial pressure of the pawl member itself can be very low and be held within limits of close toleration since the flexure of the flat spring 12 is readily predeterrninable with accuracy. Back turning of the work train during winding can therefore be eliminated. The driver wheel 6 and the pawl member 4 can be commercially made of plastic so as to minimize noise during winding, as the pawl rides over the toothed wheel in slipping direction as well as to hold production costs to a very small amount. The assembly of the individual parts i.e. the placing of the pawl on the shaft and addition of the spring 12 is so simple that it can greatly reduce production costs.

In order to make the pawl quieter it has been found that the slot receiving the pin 3 be sloped somewhat in the direction of the teeth as at 8 and this helps permit disengagement of the teeth when the disc 1 is turned to winding position. The angle of slope is preferably approximately that of the lifting face of the teeth of the drive wheel.

I claim:

1. A drive pawl member for electrically wound timepieces for transmitting unidirectional torque from an axially oscillatory member to a ratchet toothed drive wheel of a work train shaft, said pawl member being of plastic and having a shank portion provided with a slot shaped bearing opening receiving said shaft in one portion for permitting the member to rotate about said shaft and to move additionally in the direction of substantially only one straight line, said member being of L-shaped cross section to provide an upstanding end portion remote from the opening, said upstanding end portion being provided with a arcuate set of ratchet teeth substantially mating with the teeth of the drive wheel and generally directed toward the axis of the shaft, and normally generally straight spring traversing the shaft and having opposite ends substantially disposed on the pawl member, mounting means on the pawl member for holding two portions of the spring in position for urging the spring against the shaft in the direction of said upstanding portion whereby said portion is urged toward the wheel, said pawl member being provided with a drive slot generally radial to the axis of said shaft, and a pin on said oscillatory member and gyratory about the axis thereof received in the drive slot to transmit oscillatory motion of the last mentioned member to the pawl member.

2. A pawl member as claimed in claim 1, said mounting means including means for limiting movement of the spring transverse to the shaft, said shaft being provided with a circumferential groove receiving the spring, to prevent movement of the spring in the direction of the shaft axis, and slotted means on the pawl member opening away from said upstanding portion receiving the spring to retain the pawl member on the shaft.

3. A pawl member as claimed in claim 1, said drive slot being sloped and somewhat at the angle of the lifting faces of the drive wheel teeth.

4. A pawl member as claimed in claim 2, said spring being a normally flat wire-like spring.

References Cited UNITED STATES PATENTS 2,024,115 12/1935 Schwartz 74-575 2,088,794 8/1937 Kenerson 58--27 2,983,161 5/1961 Watson 74-577 3,115,788 12/1963 Siefert 74-577 FRED C. MATTERN, JR., Primary Examiner.

W. S. RATLIFF, Assistant Examiner. 

